Covertible or semifluidized beds are known per se. We previously patented a method of operating such beds for interactions between fluids and the solid particles forming the bed, including both chemical reactions and physical fluid-solid contact processes. (See Fan and Wen U.S. Pat. No. 3,374,052, issued Mar. 19, 1968.) In general, any bed of solid particles which is capable of fluidization can be employed as a convertible or semifluidized bed in the manner described in our U.S. Pat. No. 3,374,052. Also described in our prior patent is an apparatus system for operating the convertible beds.
The apparatus includes a vertically-extending column providing a cylindrical bed section supported above a fluid distributor plate or other means for introducing the fluid (gas or liquid) into the bottom of the bed. The top of the bed is restrained by an upwardly movable foraminous plate, which, typically, is a sieve plate. The amount of fluidization occurring in the bed can range from zero fluidization (fixed bed) to total fluidization by lowering or lifting the sieve plate, while the fluid is being introduced at a flow rate greater than the minimum fluidization velocity for the bed. At a given fluidization velocity less than the maximum fluidization velocity, the sieve plate can be lowered to a point where the entire bed is essentially fixed. Then by raising the sieve plate gradually the lowermost portion of the bed is first fluidized, and as the raising of the sieve plate continues, a progressively increasing portion of the bed becomes fluidized. At the same time, the fixed portion of the bed adjacent the underside of the sieve plate becomes progressively smaller until, finally, a condition is reached where the sieve plate exerts no restraint, and the entire bed is fluidized. When the sieve plate is lifted above the fluidized bed to provide a freeboard space therebetween the entire bed becomes fluidized, as in standard fluidized bed operation. In this condition, the only limitation is that the fluid velocity must not exceed the maximum fluidization velocity at which the bed has expanded to the point that it can no longer be maintained as a bed, the particles of the bed near the upper surface being carried out with the fluidizing fluid. These parameters and the method of calculating and/or experimentally determining them are well known in the art of operating fluidized beds.